A nanofibrillar cellulose hydrogel has been found use in different applications such as in cosmetics and pharmaceuticals as well as in cell growth medium. However, the use thereof in cosmetic or pharmaceutical products or devices put challenges on ensuring that the hydrogel is aseptic or sterile as well as on its other properties that may be affected by the used sterilization procedure.
Generally, sterilization efficiency is defined as the ability to remove or destroy all forms of microbial life, including viruses, bacteria and fungi, under vegetative forms or spores. However, since absolute sterility cannot be verified, the statistical definition of sterility is used in practice, by using the security assurance level (SAL), defined as “the probability of a single viable micro-organism occurring in or on a product after sterilization”. The worldwide accepted definition of sterility of medical devices is defined as the chance of finding a viable organism in or on a medical device to be at most 1 in 1000000 or an SAL of at most 10−6.
The number of viable micro-organisms in nanofibrillar cellulose hydrogel can be reduced or eliminated by subjecting the hydrogel to autoclaving for 20 minutes at a temperature of 121° C. Autoclaving, however, has some challenges as it affects the properties, such as viscosity, of the hydrogel.
The inventors have therefore recognized the need for a method to treat nanofibrillar cellulose hydrogel such that it is suitable for further applications.